1. Field of the Invention
The present invention relates to a reciprocatory piston type compressor with an improved suction valve mechanism, and used in a unit for air-conditioning a vehicle passenger compartment, and more particularly, to a reciprocatory piston type compressor with a suction valve mechanism free from the irregular vibration which is a cause of noise in the compressor and pulsation in the flow of a suction refrigerant gas.
2. Description of the Related Art
Many piston type compressors, such as a swash plate type compressor and a wobble are known. For example, U.S. Pat. No. 4,691,526 to Kobayashi et al discloses an air-conditioning unit for a vehicle employing a multi-cylinder swash plate type compressor with double-acting reciprocatory pistons and front and rear suction valve mechanisms having a valve plate for defining suction and discharge ports, and a valve sheet defining therein resilient reed valves, respectively. U.S. Pat. No. 4,687,419 to Suzuki et al discloses a multi-cylinder variable displacement wobble plate type compressor with double-acting reciprocatory pistons and a suction valve mechanism similar to the suction valve mechanism of the swash plate type compressor of U.S. Pat. No. 4,691,526. Each of the known multi-cylinder swash plate type and wobble plate type compressors of U.S. Nos. 4,691,526 and 4,687,419 includes a cylinder block having a plurality of cylinder bores serving as compression chambers to permit double-acting pistons to be reciprocated therein to compress a refrigerant gas. Both ends of the cylinder block of U.S. Nos. 4,691,526 are closed by front and rear housings, via valve plates, so that suction and discharge chambers are formed in each of the housings. The suction chambers are fluidly communicated with the compression chambers through a suction valve mechanism including suction ports formed in the valve plates, and suction valves arranged on the inner side of the valve plates, and the discharge chambers are fluidly communicated with the compression chambers through a discharge valve mechanism including discharge ports formed in the same valve plates, and discharge valves arranged on the outer side of the valve plates. The valve plates are also formed with inlet ports, to permit a refrigerant gas returning from the outer air-conditioning circuit to flow into the suction chambers, and outlet ports to permit a compressed refrigerant gas to flow from the discharge chambers into the air-conditioning circuit. Similarly, both ends of the cylinder block of U.S. Pat. No. 4,687,419 are closed by front and rear housings. However, only one of the housings (rear housing) is attached to one end of the cylinder block, via a valve plate, so that suction and discharge chambers are formed in the rear housing. The suction and discharge chambers are fluidly communicated with the compression chambers of the cylinder block through suction and discharge valve mechanisms similar to those of U.S. Nos. 4,691,526.
A typical construction and arrangement of the above-mentioned conventional suction valve mechanism is illustrated in FIGS. 6 through 9.
FIG. 6 shows one of plurality of cylinder bores 1b of a cylinder block 1 of a swash plate type or wobble plate type compressor. The cylinder bores 1b are equiangularly arranged around the center of the cylinder block 1, and receive a corresponding number of pistons therein (not illustrated in FIG. 6) which are reciprocated in response to the rotation of a swash plate or wobble plate as illustrated in U.S. Pat. No. 4,691,526 or 4,687,419. The cylinder block 1 has one end la to which a suction valve sheet 2 made of, e.g., a resilient thin metallic sheet, and a thick valve plate 3 are firmly attached, and closed by a housing 12. The housing 12 defines therein an inner discharge chamber 12A and on outer suction chamber 12B. The valve plate 3 is provided with a plurality of equiangularly arranged suction ports 4 for communicating between the suction chamber 12B and the plurality of cylinder bores 1b, and a plurality of equiangularly arranged discharge ports 5 for communicating between the plurality of cylinder bores 1b and the discharge chamber 12A. As illustrated in FIG. 7, the suction valve sheet 2 has a plurality of resilient suction valves 2a to open and sealingly close the suction ports 4. Each of the plurality of resilient suction valves 2a of the suction valve sheet 2 is formed as a reed valve radially extending from a central portion to an outer portion of the suction valve sheet 2, and surrounded by a pair of cutaway portions 7 on opposite sides of a wide base portion of the suction valve 2a and a cutoff slot 11 extending between the pair of cutaway portions 7 along both slanting sides 2ab and a free end 2aA of the suction valve 2a. The suction valve 2a has an aperture 2b formed in the base portion thereof in registration with the discharge port 5 of the valve plate 3. The free end 2aA of each resilient suction valve 2a is resiliently bent and moved away and separated from the valve plate 3 under a pressure difference between pressures within the cylinder bore 1b and the suction chamber 12B during the suction stroke of the corresponding reciprocating piston in the cylinder bore 1b. In the separated state, the free end 2aA of the suction valve 2a is abutted against a wall 6a of a radial recess 6 formed in an end 1a of the cylinder block 1 at a portion disposed adjacent to the end of the cylinder bore 1b, as illustrated in FIG. 9.
In FIG. 6, a plurality of discharge valves 8 (one of which is shown in FIGS. 6, 8 and 9, respectively) and the corresponding number of valve retainers 9 are arranged in the discharge chamber 12A of the housing 12 and secured to the valve plate 3 on the side thereof confronting the discharge chamber 12A by a screw bolt 10. The discharge valves 8 are arranged so as to open and close the corresponding discharge ports 5 of the valve plate, and are resiliently opened by the pressure of the compressed refrigerant gas during the discharge stroke of the related reciprocatory pistons in the cylinder bores 1b. The amount of the opening of each discharge valve 8 is controlled by the associated retainer 9.
At this stage, it should be understood that the cutoff slot 11 separating the free end 2aA of each resilient suction valve 2a from an edge 2c of the suction valve sheet 2 is very narrow and has a width L.sub.1 as best illustrated in FIG. 7. Therefore, when the operation of the piston type compressor starts, i.e., when each reciprocatory piston reciprocates in each cylinder bore 1b, the suction, compression and discharge strokes of the piston are repeatedly carried out in each cylinder bore 1b. When the discharge stroke is switched to the subsequent suction stroke, each resilient suction valve 2a of the suction valve sheet 2 is bent to an open position thereof by the pressure difference between a reduced pressure within the cylinder bore 1b and a pressure prevailing in the suction chamber 12B of the housing 12 as illustrated in FIG. 9. Thus, the corresponding suction port 4 of the valve plate 3 is opened to allow the refrigerant gas in the suction chamber 12B to be drawn into the cylinder bore 1b.
When the suction stroke is switched to the compression stroke, each resilient suction valve 2a of the suction valve sheet 2 resiliently returns to the closed position, to close the corresponding suction port 4 of the valve plate 3 under a high pressure of the compressed refrigerant gas, and the associated discharge valve 8 is moved to the open position to open the discharge port 5 of the valve plate 3 by the high pressure of the compressed refrigerant gas.
With the above-described construction and operation of the conventional suction valve mechanism of the reciprocatory piston type compressor, the cutoff slot 11 of the suction valve sheet 2, especially a part of the cutoff slot 11 located adjacent to the free end 2aA of each suction valve 2a, is made narrow to prevent a reduction in the compression efficiency of the compressor. Therefore, when the compressor is driven by a vehicle engine at a low rotating speed, such as an idling speed, the suction pressure of the compressor is maintained at a low level. Thus, the suction valves 2a of the suction valve sheet 2 cannot be smoothly bent toward the open position from the closed position in contact with the face of the valve plate 3, due to a lack of pressure difference between pressures in the suction chamber 12B and respective cylinder bores 1b. Further, an oil mist attached to the contacting faces of the suction valves 2a and the valve plate 3 prevents an immediate separation of the suction valves 2a from the face of the valve plate 3 at an initial stage of the suction stroke, as best illustrated in FIG. 8, and with the proceeding of the suction stroke, the suction valves 2a are abruptly separated from the contacting face of the valve plate 3. As a result, the free ends 2aA of the suction valves 2a hit hard against the corresponding walls 6a of the radial recesses 6 of the cylinder block 1, to produce a loud noise. The loud noise further produces an unpleasant resonance which is transmitted through the cylinder block 1.
On the other hand, regardless of the proceeding of the suction stroke, if the free ends 2aA of respective suction valves 2a do not bend enough to hit the corresponding walls 6a of the radial recesses 6 of the cylinder block 1, due to a lack of suction pressure for attracting the free ends 2aA toward the walls 6a of the radial recesses 6, the suction valves 2a carry out a self vibration between the closed and open positions, due to the balance of the suction pressure and the resiliency of the suction valves 2a per se, and thus a smooth suction of the refrigerant gas from the suction chamber 12B to the cylinder bores 1b is prevented.
In addition, when the vibration of the suction valves 2a occurs during the suction stroke of the reciprocatory pistons of the compressor, a large pulsation appears in the suction stream of the refrigerant gas, causing noise as well as a reduction in the compression performance of the compressor.